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From a source of 12V,3A capacity, how it is possible to reduce voltage to 5-8V with constant supply of 3A current to load?

yv nitesh
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    The question doesn't make sense. If you want a useful answer, you'll have to explain yourself better. – Dampmaskin Jan 05 '18 at 15:16
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    A constant current source? Is that what you want? – Rohat Kılıç Jan 05 '18 at 15:22
  • What is the load? – The Photon Jan 05 '18 at 15:45
  • @TomCarpenter I think OP is looking for a constant-current regulator rather than a power supply, he already gave values for one that make sense for his load. – pserra Jan 05 '18 at 16:06
  • @pserra I read it as "I have power supply of X voltage and need to change it to Y voltage without changing current rating.", in which case much of the details are covered in the linked q. Probably me misreading it. – Tom Carpenter Jan 05 '18 at 16:46
  • If you have 12V 3A DC battery and you need to operate a device of operating voltage range from 5-8V then keeping current constant, how we can reduce voltage? – yv nitesh Jan 05 '18 at 17:12
  • What is the load? The way you've asked the question is very confusing and contradictory, probably because you don't understand the exact meanings of some of the words you're using. That's okay, but we can't give you a reliable answer, and you should not trust any of the answers you've gotten, until you tell us what the load actually is. – The Photon Jan 06 '18 at 02:01
  • We need to operate arduinoof operating voltage 5-8V with 12V 3A battery but want to keep current constant. So how can it be done? – yv nitesh Jan 06 '18 at 07:42

2 Answers2

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If it is a constant current source that you need, there are several ways to build one. Each one has its advantages, and the subject is very broad. Maybe if you explain your specific issue, experienced users will direct you.

One of the most common and straightforward ways to regulate the current is to use an integrated circuit like the LM350 or similar ones. Very common in hobby projects, and if you google around you can find many guides and tutorials.

Please notice that any approach you choose, since you will be now controlling the current, the voltage will become the dependent variable of your circuit, and for linear circuits Ohm's law still applies! So the voltage will still be the product between the circuit impedance Z and the current you are regulating. You are not necessarily getting a 5 V or 8 V voltage, it depends on the circuit.

(By simplifying a bit, impedance Z is the same thing as resistance R, as long as you only have DC)

sEdivad
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schematic

simulate this circuit – Schematic created using CircuitLab

You can find the value of R1 with ohm's law. Whit linear regulators, the current to the ADJ pin is small and can be set to 0 for your calculations.

pserra
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